1. Field of the Invention
The present invention relates to a semiconductor light source for emitting a light beam of two different wavelengths and an optical pickup head apparatus and a data record/playback apparatus for storage, playing back, and erasing data on an optical disk.
2. Description of the Related Art
Optical disks are known as high-density, mass-storage mediums on which data is stored in the form of a pattern of bits. The optical disks are classified into various types depending on the contents of data and the application. Characteristic examples of the optical disks are digital audio disks, video disks, text file disks, data file disks and so forth. Their applications are now increased as they are spread into in different fields. In particular, digital versatile disks (DVD) are popular and get focused as high-density optical disks for using 650 nm wavelength visible light emitted from a semiconductor laser. The DVD disks are available in different formats including read only DVD-ROM, once writable DVD-R, and rewritable DVD-RAM. Also, compact disks (CD) are widely known using a 780 nm wavelength infrared light emitted from a semiconductor laser. Similar to the DVD, the CD disks are available in different formats including read only CD-ROM, once rewritable CD-R, and multiply rewritable CD-RW.
As both DVD and CD are popular, it is desired for the convenience of any user to play back data from not only DVD-ROM and CD-ROM, but also DVD-R and CD-R with the use of a single data playback apparatus.
The CD-R and DVD-R technologies are similar to each other in storage and playing back data on the basis of different levels of the reflectivity of colors. However, the reflectivity and the absorptance are optimized in narrow wavelength ranges about 780 nm and 650 nm, respectively. This disallows CD-R data to be read and played back using the 650 nm wavelength light beam. Also, DVD-R data is hardly permitted to be read and played back using the 780 nm wavelength light beam. For compensation, each CD-R/DVD-R compatible type data record/playback apparatus has an optical pickup head equipped with a DVD-R accessible semiconductor laser and a CD-R accessible semiconductor laser.
For minimizing the overall size and the production cost of the data record/playback apparatus, the optical pickup head should be decreased in the size and the cost. One of such techniques is proposed for integrating the above described two different wavelength semiconductor lasers into a single package to simplify the optical system of the optical pickup head,
FIG. 16 illustrates an arrangement of a conventional optical pickup head apparatus 1600 such as disclosed in Japanese Patent Laid-open Publication (Heisei)10-289468. The optical pickup head apparatus 1600 has a light source 110 and a light source 120 both provided on a substrate 610 in a package 60 for emitting a beam of linearly polarized divergent light having a wavelength of 650 nm and a beam of linearly polarized divergent light having a wavelength of 780 nm, respectively.
The principle of a method of reading data from a storage medium 20 with the optical pickup head 1600 will now be explained. A light beam 100 emitted from the light source 110 or 120 is first directed to a beam composite means 30 which may be implemented by a polarizing prism (a birefringent plate) or a hologram. The beam composite means 30 aligns any light beam from either the light source 110 or the light source 120 with the optical axis. When the light beam 100 is received from the light source 120, it is refracted or diffracted by the beam composite means 30 for deflection. The light beam 100 is then converted to a collimate light by a collimate lens 131, circularly polarized by a xc2xc wavelength plate 140, passed through an aperture 15, and converted to a beam of convergence light by an objective lens 132. The light beam 100 is directed to the optical storage medium 20 and more specifically, passed through a transparent substrate 21 and focused on a data recording surface 22. The light beam 100 is reflected on the data recording surface 22, converted by the xc2xc wavelength plate 140 to a polarized beam shifted 90 degrees from the onward beam, passed through the beam composite means 30, and received by deflecting means 40 (a polarizing hologram) before guided to a photo detecting means 50. A signal produced by the photo detecting means 50 is used as a data signal indicative of the data for generating a focusing error signal and a tracking error signal which are then supplied to an actuator 16 for focusing and tracking control.
It is common in the data record/playback apparatus for rewritable disks such as DVD-RAM that the tracking control signal is unstable because of shallow pits of the disks. For compensation, a diffraction grating (not shown) is provided for generating three different diffracted lights to determine the focusing error signal and the tracking error signal.
As the conventional optical pickup head apparatus 1600 includes the beam composite means 30 of a polarizing prism or hologram and the xc2xc wavelength plate 140 for handling the polarized light, its optical system will significantly increase in the cost.
When the transparent substrate 21 of the optical storage medium 20 is birefringent, the light beam reflected on the optical storage medium 20 may be deflected by the beam composite means 30 and hardly received by the photo detecting means 50 which thus fails to read data from the optical storage medium 20.
Also, while the two light sources 110 and 120 are provided on the single substrate 610, there may be less a room for the diffraction grating which is arranged for generating three different diffracted lights and should be controlled properly. The overall dimensions of the optical pickup head apparatus itself will be increased.
It is, hence, an object of the present invention to provide a semiconductor light source package, an optical pickup head apparatus, and an optical data apparatus where a non-polarizing prism is used for minimizing the number of components and thus the overall cost. It is another object of the present invention to provide an optical pickup head apparatus and an optical data apparatus where desired data can be read out from an optical storage medium 20 while the tracking error signal is appropriately produced, even though the transparent substrate of the optical storage medium is birefringent.
A light source package according to the present invention comprises: a first light source which emits a first light beam; a second light source which emits a second light beam which is different from the first light beam; and a deflection arrangement which deflects the first and second light beams and releases the deflected light beam as a third light beam, wherein the deflection arrangement includes a first deflector which deflects the first light beam and a second deflector which deflects the second light beam such that the optical axis of the first deflected light beam from the first deflector and the optical axis of the second deflected light beam from the second deflector substantially coincide.
An optical pickup head apparatus according to one aspect of the present invention comprises: a first light source which emits a first light beam having a wavelength xcex1; a second light source which emits a second light beam having a wavelength xcex2 which is different from the wavelength xcex1; a diffractor which generates a plurality of light beams from the light beam emitted from the light source; a light converging unit which converges the plurality of light beams received from the diffractor on an optical storage medium; a beam splitter which deflects the plurality of light beams converged and reflected on the optical storage medium; and a photodetector which receives deflected light beams from the beam splitter and outputs a signal relative to intensity of the deflected light beam, wherein the diffractor includes a first pattern and a second pattern provided at an angle to each other, the first pattern having a higher diffraction efficiency of a beam having a wavelength xcex1 than that having a wavelength xcex2 and the second pattern having a higher diffraction efficiency of a beam having a wavelength xcex2 than that having a wavelength xcex1.
An optical pickup head apparatus according to another aspect of the present invention comprises a beam splitter which deflects a light beam converged and reflected on a optical storage medium; and a photodetector which generates and releases a signal indicative of the intensity of each of the deflected light beams received from the beam splitter, wherein the beam splitter is a holographic optical element including a first holographic pattern and a, second holographic pattern, the first holographic pattern having a higher diffraction efficiency of a beam having a wavelength xcex1 than that having a wavelength xcex2 and the second holographic pattern having a higher diffraction efficiency of a beam having a wavelength (2 than that having a wavelength xcex1.
Also, a data record/playback apparatus of the present invention may be provided, which comprises: one of optical pickup head apparatuses according to the present invention; a drive which varies the position of the optical pickup head apparatus relative to a data storage medium; and an electric signal processor responsive to a signal received from the optical pickup head apparatus which performs an arithmetic operation to reconstruct a desired data. Accordingly, an optical data apparatus can be implemented which allows the intensity of each light received by its photodetector to remain unchanged when an optical storage medium to be played back is partially birefringent, hence ensuring improved playback of data.
Also, during the assembling of the optical pickup head apparatus, the diffraction grating is adjustably positioned to match one of any two formats, CD and DVD, of the optical storage medium while its adjustment for the other format is automatically done at the same time. As a result, the optical pickup head apparatus will be highly improved in the productivity.